1. Field of the Invention
The present invention relates to a neon discharge lamp, and more particularly to a neon discharge lamp of which the life of the lamp is extended and for use in an indicating lamp, an advertising lamp and the like utilizing a relatively long operating life provided thereto.
2. Background Art
FIG. 4 illustrates an exemplary configuration of a 15 conventional neon discharge lamp 90 of this kind. This neon discharge lamp 90 is comprised of a tubular bulb 91 and a pair of mounts 92 sealing respective ends thereof. The mount 92 is comprised of a plate electrode 92a, a nickel wire 92b, a Dumet wire 92c and a bead 92d. Neon gas 93 is sealed within the tubular bulb 91 at a pressure of about 100 Torr.
When an A.C. voltage is applied across the plate electrodes 92a of the neon discharge lamp 90 thus constructed, the neon discharge lamp is lit by gas discharge.
The plate electrode 92a includes ZrAl getters for adsorption of impurity gases generated during illuminating in order to prevent the operating life of the neon discharge lamp from being shortened.
There are some other Phenomena which shorten the operating life of the neon discharge lamp 90 other than the generation of the impurity gases aforementioned. There is a known process of cathode sputtering as schematically shown in FIG. 5. Fine particles 92e generated from the plate electrode 92a material by electric discharge sputter toward the inside wall of the tubular bulb 91 and are attached there. During this process, the pressure inside the tubular bulb 91 reduces, since some of neon gas 93 inside the tubular bulb 91 is encompassed by the fine particles 92e which are attached to the inside of the tubular bulb 91. Thus, the operating life of the neon discharge lamp is shortened.
Particularly, in the cathode sputtering mentioned above, if the gas pressure decreases, the sputtering of the plate electrode 92a material tends to increase, and, therefore, the amount of neon gas encompassed by the fine particles 92e increases even more. Thus, the decreasing of the gas pressure accelerates the sputtering of the plate electrode 92a material and shortens the operating life of the neon discharge lamp.
Furthermore, the electrode material thus sputtered and attached decreases the transparency of the tubular bulb 91, leading to the phenomenon of the so-called blackening. These phenomena leading to loss of lighting amount accelerate the shortening of the operating life of the neon discharge lamp.
For the conventional neon discharge lamp 90 mentioned above, measures have been taken only for the shortening of the operating life of the neon discharge lamp caused by impurity gases and no measures have been taken for the shortened life caused by the sputtering. Thus, the problem of the sputtering still remains to be solved and the need exists for an even longer operating life of the neon discharge lamp.